I would be surprised if the suitcases were stored inside the house but somewhere in a shed, garden shed or garage outside. Who would happily put up with that extra clutter for that many years?
Why am I thinking a shipping container would be a perfect airtight environment to store a decomposing body away from enquiring eyes and noses.
Could have used a storage facility. They are lock up and no one looks in them unless the fee is not paid.